I wrote a story for The Post yesterday about the six-minute clip from the Brazilian TV hidden-camera show, “Pegadinha” — in which a ghostly young girl, holding a bald doll, terrifies unsuspecting “victims” in an elevator.

When I wrote that story, nearly 7 million people had watched the clip on YouTube in just under 48 hours. That number, as of yesterday, had jumped to over 16.5 million hits.

So what gives?

Scott Hallock, the co-creator/executive producer of Syfy’s “Scare Tactics,” knows a thing or two about cartoonishly creepy hidden-camera pranks, since his show (currently hosted by Tracy Morgan), has specialized in this genre since 2003. He thinks the elevator prank’s effectiveness is heightened because “Pegadinha” producers apparently chose their “victims” at random — unlike “Scare Tactics,” which uses accomplices to corral friends and family members to participate.

“We pre-screen all our ‘marks,’ since the last thing we want to do is scare someone with a heart condition or someone who has a phobia about bugs or is claustrophobic,” Hallock says. “Apparently this prank was pulled on random people who haven’t been screened.”

The joke in the “Pegadinha” prank is that viewers at home can see the young actress sneaking into and out of the mirrored elevator through a trap door — as the lights go out — before she scares the bejeezus out of her prey (both men and women, alone and in pairs).

Hallock says that “Scare Tactics” has wanted to do an elevator prank for some time, but has never been able to pull it off — another reason why the “Pegadinha” clip strikes a chord.

“The fact that they turn the lights out and sneak the girl into the elevator and then turn the lights on is extremely effective and scary,” he says. “We’ve wanted to do an elevator prank on ‘Scare Tactics’ forever but haven’t been able to find the right elevator setup,” he says. “It looks like they had a fantastic location . . . and to be able to have access to the back of the elevator, to sneak someone in and out while the lights were out, is a perfect idea.”

Hallock also says that, well, there’s just something about little kids that generates fear in people.

“We’ve used little kids to scare people many times, and it’s extremely effective,” he says. “People are just creeped out by little kids — especially when you add being trapped in an elevator with a creepy little girl holding a bald baby doll.”

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Last, but not least:

* CBS has ordered 13 episodes of “Under the Dome,” a drama based on Stephen King’s novel of the same name. It will air next summer . . . USA Network has launched its “Burn Notice Science Challenge” competition, which gives high school students nationwide the chance to test their science knowledge and creativity. The contest runs through Feb. 15 . . . A&E’s “Duck Dynasty” broke another series record Wednesday night, snaring 4.9 million viewers at 10:30 . . . Hallmark Channel has surpassed 1 million fans on Facebook. Must be all those holiday movies — you know, “The Fill-in-the-Blank That Saved Christmas.” I tease them a lot over there, but they’re obviously doing something right. Rock on.